Apparatus for making bends in tubing



May 10, 1966 F. J. FUCHS, JR 3,250,112

APPARATUS FOR MAKING BENDS IN TUBING Filed Oct. 10, 1965 4 Sheets-Sheet 1 I! I I INVENTOR fiazzazls' JMgJ;

ATTORNEY 4 Sheets-Sheet 2 May 10, 1966 F. J. FUCHS, JR

APPARATUS FOR MAKING BENDS IN TUBING Filed Oct. 10, 1963 y 1966 F. J. FUCHS, JR 3,250,112

APPARATUS FOR MAKING BENDS IN TUBING Filed Oct. 10, 1963 4 Sheets-Sheet 5 y 0, 1966 F. J. FUCHS, JR 3,250,112

APPARATUS FOR MAKING BENDS IN TUBING Filed Oct. 10, 1963 4 Sheets-Sheet 4 [Illllllllllllllllllll]. I), 0

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United States Patent This invention relates to apparatus for making bends in tubing and more particularly to a mandrel forsupporting the interior of rectangular tubing while effecting a seamless bend. While the mandrel of this invention is useful in bending any rectangular tubing, it finds speas free as possible from cavities below the neutral axis of the bend so that portions of the tubing in compression will not flow inwardly and produce interior surface irregularities.

In the past, seamless miter bends have been formed in tubing by two or three step bending operations and involved the use of separate m'andrels for supporting the inner walls of the tubing during each bending operation. The mandrel of this invention permits seamless miter bends to be formed by a single bending operation. This is accomplished by providing the mandrel with surfaces including movable dies for supporting the inner walls of the tubing.

It is an object of the present invention to provide a new and improved mandrel.

It is another object of the present invention to provide a bending mandrel having a minimum of cavities below the neutral axis and having facilities for maintaining these cavities at a minimum during bending.

It is a further object of the present invention to provide a mandrel having relatively movable dies with facilities for maintaining these dies in a desired configuration during insertion into a tube to be bent and during bending.

With these and other objects in view, the present invention contemplates a mandrel having surfaces for supporting the inner walls of a tube during bending. The mandrel may include, for example, a pair of rectangular bars with disc dies having complementary interlocking surfaces rotatably mounted on the inner ends thereof. A pair-of slide dies with pivotally mounted link dies on the ends thereof may be slidably secured to the bars for supporting the underside of the tube during bending. Recesses may also be provided in the disc dies adjacent the underside of the tube and facilities for urging the ends of the link dies into the recesses.

Other objects and advantages of the present invention will be apparent from an examination of the following detailed description when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a plan view schematically showing a bending machine suitable for use with the mandrel of this invention;

FIG. 2 is a perspective view of a rectangular waveguide tube having a miter bend and dimples;

FIG. 3 is a perspective view of a mandrel for supporting the interior of a tube during bending which is constructed in accordance with the principles of the present invention;

FIG. 4 is a partially sectional plan view of the mandrel shown in FIG. 3 illustrating the disc and slide dies;

- present invention.

3,250,112 Patented May 10, 1966 FIG. 3 inserted withinand supporting a tube having twobends of 45 degrees each; and

FIG. 10 is a fragmentary view of the mandrel shown in FIG. 3 partially withdrawn from the bent tube shown in FIG. 9. t

In FIG. 2 there is shown a rectangular tube 10'having a seamless miter bend. The bend is formed by bending end sections 11 and 12 of tube 10 at angles of 45 degrees from the center section 13. This type of bend is commonly known as a degree miter bend. The tube 10 also has dimples 15 and 16 in the upper surface to improve the electrical characteristics thereof for waveguide use.

In FIG. 1 there is schematically shown a bending apparatus 18 comprising a pair of arms 19 and 20 pivotally mounted on pins 22 and 23 which extend upward from a base 24. The arms 19 and 20 each have depending projections (not shown) which ride in guide slots 26 and 27 formed in the base 24. Links 28 and 29 connect the arms 19 and 20, respectively,'to a drive block 31 which may be advanced along bar 32 to pivot the arms about the pins 22 and 23. I

The arms 19 and 20 are provided with substantially rectangular slots 33 and 34 for receiving a length of straight rectangular tubing to be bent. Punches 35 and 36 may be advanced into slots 33 and 34 to form dimples in a bent tube.

In FIG. 3 there is shown an embodiment of a rectangular mandrel 38 which forms the subject matterof the The mandrel 38 generally comprises mandrel halves or-rectangular bars 41 and 42. The bars 41 and 42 are comprised of rectangular bar sections 43, 44, 45, and 46 and are provided .with rectangular end caps 47 and 48. Disc dies 51 and 52 are pivotally mounted on pins 53 and 54 to the bars 41 and 42. Disc die 51 has a convex projecting surface 56, and disc die '52 has a concave surface 57 which is complementary to and may be interlocked with projecting surface 56.

Tapered slide dies 58 and 59 are slidably held in dovetail slots 61 and 62 in the undersides of bar sections 44 mounted on pin 54 to the bar 42.

As seen in FIG. 3, bar sections 44 and 45 have smaller widths W than bar sections 43 and 46 and have tapered lower surfaces 74 and 76. The tapered surfaces 74 and 76 are dimensioned so that together with the tapered slide dies 58 and 59 the bar sections 44 and 45 complete a rectangular cross section substantially the same size as that of bar sections 43 and 46.

As seen in FIG. 7 in plan view, when disc dies 51 and 52 are interlocked, the disc dies together with foot die 73 and link dies 63 and 64 fit together to form a substantially continuous rectangular surface. As can be seen in FIG. 3, this continuous surface is rectangular and has a cross sectionsubstantially the same as that of the bar sections 43 and 46.

Referring to FIG. 4, disc dies 51 and 52 are show mounted on pins 53 and 54 which extend between the walls of the disc dies in apertures 55 and 56, respectively 4 suitable bolts (not shown).

(FIGS. 5 and '6). Pins 53 and 54 are in turn seated within holes in lugs-78 and 79 which lugs are fixed in bores 81 and 82 in bar sections 44 and 45, respectively. Lug 79 has a bifurcated end for receiving arm 83 which extends from foot die 73 to pivotally mount the foot die about pin 54.

7 Bar sections 43 and 44 are held together by a bolt 86 inserted in apertures 87 and 88 in the bar sections. End cap 47 is secured to bar section 43 by suitable bolts (not shown). A wire 90 is connected to disc die 51 by a pm 91 which is seated in apertures 92 (FIG. 5) in the walls of disc die 51. The wire 90 extends through bores 93 and 94 in the sections 43 and 44, and is fixed to a plunger 96.

" Compression spring 97 urges the plunger 96 to the left as seen in FIG. 4 tending to rotate the disc die 51 counterclockwise.

Similarly, bar sections 45 and 46 are held together by a bolt 101 inserted in apertures 102 and 103 in the bar sections. End cap 48 is secured to bar section 46 by A wire 105 is connected to disc die 52 by a pin 106 which is seated in apertures 107 (FIG. 6) in the Walls of disc die 52. The wire 105 extends through bores 108 and 109 in the sections 45 and 46, and is attached to a plunger 111. Compression spring 112 urges plunger 111 to the right as viewed in FIG. 4 tending to rotate disc die 52 clockwise.

A wire 114 is connected to foot die 73 and extends through bores 115 and 116 in the bar section 45 and 46, respectively, and through a bore 117 in a plunger 118 and is connected to a plunger 119. Compression spring 121 urges plunger 119 to the right, as seen in FIG. 4,

tending to rotate foot die 73 counterclockwise.

In FIG. 7 there is shown a tube 123 having a neutral 5 bending axis 124 i.e. the plane above which the tube will be in tension and below which the tube will be in compression during bending. Disc dies 51 and 52 have shoulders 125 and 126 above the neutral axis 124 in engagement with abutments 127 and 128 formed above the neutral axis in the bar sections 44 and 45. Abutments 127 and 128 limit the rotation of disc dies 51 and 52 in the counterclockwise and clockwise directions, respectively. Disc die 52 (FIGS. 4 and 6) has abutment 129 between the walls of the die which limits'the rotation of arm 83, thus of foot die 73, in the counterclockwise direction.

The abutments 127 and 128 are dimensioned so that 7 upper surfaces 131 and 132 (FIG. 4) of disc dies 51 and tive abutments under the influence of springs 97, 112,

and 121, and the disc dies are mated, a continuous rec- :tangular cross section identical to that of the bars is formed.

Bar 41 has a plunger 131 including a connecting pin 132 which is seated in a bore 133 in the dovetail portion of tapered slide die 58. Compression spring 134 acting on this plunger urges tapered die 58, hence link die 63, into a compartment formed by recess 71 and foot die 73 (FIG. 7). Similarly, plunger 118 in bar 42 drives a connecting pin 136 seated in a bore in the dovetail portion of tapered die 59. Compression spring 121 urges tapered die 59, hence link die 64, into a compartment formed by the recess 72 and foot die 73 (FIG. 7).

In operation a rectangular tube is inserted into slots 33 and 34 in bending machine 18 (FIG. 1) and mandrel halves 41 and 42 are inserted into opposite ends of the rectangular tube 123 which closely fits about the mandrel halves (FIG. 7). Since the outer dimensions of the mandrel are very close to the inner dimensions of the tube, sliding friction tends to move the tapered dies 58 and 59 and link dies 63 and 64 relative to the mandrel halves. The force of compression springs 134 and 121 urge link dies 63 and 64 into recesses 71 and 72 in the disc dies 51 and 52 to overcome this friction force. Friction also tends to rotate disc dies 51 and 52 and foot die 73 relative to their positions against the abutments 127, 128, and 129, respectively. The tension on wires and connected to the disc dies 51 and 52 and tension on wire 114 connected to foot die 73 holds these dies against their respective abutments 127, 128, and 129 overcoming friction forces and insuring that the dies will properly mate and interlock within the tube. Connecting pins 132 and 136 which urge link dies 63 and 64 into recesses 71 and 72 in disc dies 51 and 52, respectively, also tend to rotate the disc dies against their respective abutments and aid the action of springs 97 and 112.

With the mandrel inserted within the tube (FIG. 7) and the disc dies 51 and 52 mated and interlocked, the slide, link, and foot dies are in position to support the underside of the tube, and the disc dies and bar sections 44 and 45 are in position to support the upperside of the tube during bending. Guide block 31 (FIG. 1) is now advanced along bar 32 to rotate arms 19 and 20 about pivot pins 22 and 23 to initiate bending.

In FIG. 8 ends 136 and 137 of tube 123 have each been bent 22 /2 degrees with respect to the center portion 138 of the tube. Bar sections 44 and 45 have also rotated with respect to disc dies 51 and 52 exposing cavities 141 and 142 between shoulders and 126 of disc dies 51 and 52 and abutments 127 and 128 of the bar sections. Since the abutments 127 and 128 are above the neutral axis during bending, and the portion of the tube above the neutral axis is in tension during bending, the tube in this area will not tend to fiow inwardly into these cavities producing surface irregularities.

In FIGS. 7 and 8, relief cavities 143 and 144 are shown between disc dies 51 and 52, bar sections 44 and 45, and tapered dies 58 and 59 for receiving lower ends 145 and 146 of bar sections 44 and 45 during bending. As seen progressively in FIGS. 7, 8, and 9, ends 145 and 146 of bar sections 44 and 45 are received within relief cavities 143 and 144, until at completion of the bend (FIG. 9), the relief cavities are completely closed. Since the relief cavities 143 and 144 are below the 'neutral axis and these cavities diminish in size during bending, inward flow of the tube (which is in compression below the neutral axis during bending) is almost entirely prevented; thus, avoiding any possibilities for forming surface irregularities at this point. t

In FIG. 9, upon completion of the bend, dimpling punches 35 and 36 are advanced into the upper Wall of the tube forcing it to conform to angular indentations 151 and 152 formed in the disc dies 51 and 52, respectively. The ends 136 and 137 of the tube 123 have been bent 45 degrees with respect to the center section 138 of the tube; thus completing a 90 degree seamless miter bend. The indentations 151 and 152 have upper surfaces 153 and 154 and lower surfaces 155 and 156. The upper surfaces of the indentations are positioned at 45 degree angles with respect to the center section 138 of the tube and are parallel to the bent ends 136 and 137 of the tube. Surface 157 of foot die 73 is also positioned at a 45 degree angle with respect to the center section 138 of the tube and is parallel to the bent end 136 of the tube. Surface 157 on foot die 73 permits withdrawal of disc die 51 from the interlocked position with disc die 52. Upper surfaces 153 and 154 of the indentations formed at predetermined angles of 45 degrees permit the mandrel halves to be withdrawn from the dimples without rotation of the disc dies.

As seen in FIG. 10, after disc die 51 has been withdrawn into the bent end 136 of the tube 123, disc die 52 is next withdrawn. Surface 154 on disc die 52 permits withdrawal of the disc die from the dimple without rotation of the disc die.- Foot die 73 rotates clockwise until the lower surface 133 is parallel to the bent end 137 of the tube 123. When the mandrel halves 41 and 42, disc dies 51 and 52, and foot die 73 are wholly withdrawn from the bent ends of the tube, springs 97, 112, and 121 will again rotate disc dies 51 and 52 and toot die 73 against their respective abutments. The mandrel halves are now ready to be inserted in another tube for another bending operation.

It is to be understood that the above-described arrangements are simply illustrative of an application o-fthe principles of this invention. Numerous other arrangements may be readily-devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. A rectangular mandrel for supporting the inner walls of a rectangular tube during the bending comprising a pair of rectangular bars,

a pair of disc dies rotatably mounted on the ends of the bars, one of said disc dies having a convex projection and the other of said disc dies having a complementary interlocking concave portion, each of said disc dies having a recess adjacent the underside of the tube,

a pair of slide dies slidably secured to the bars for supporting the underside of the tube,

a pair of link dies pivotally mounted on the ends of the slide dies, and

means for urging the ends of the link dies into the recesses in the disc dies.

2. A rectangular mandrel for supporting the inner walls of a rectangular t-ub e during bending above and below the neutral axis comprising a pair of oppositely disposed rectangular bars,

a pair of disc dies mounted for rotation on the inner ends of the bars, one of said disc dies having a convex projection and the other of said disc dies having a complementary interlocking concave portion,

a foot die rotatably mounted on one of said bars, said foot die and disc dies mating to form a rectangle of the same size as the bars, and

means for normally positioning said disc dies and foot die to align the dies to mate in the form of said rectangle.

3. A mandrel tor supporting rectangular tubing during bending above and below the neutral axis comprising a pair of rectangular bars slidab-ly insertabie into opposite ends of a tube to be bent,

a pair of discs dies rotatably mounted on the inner ends of the bars, one of said disc dies having a convex surface and the other of said disc dies having an interlocking complementary concave surface, said disc dies having angular indentations above the neutral axis conforming to a desired configuration in the upperside of the bent tube and recesses below the neutral axis adjacent the underside of the tube,

a pair of slide dies slida bly mounted below the neutral axis on the bars for supporting the underside of the tube,

a pair of link dies pivotally mounted on the inner ends of the slide dies,

a foot die rotatably mounted on one of said bars, said foot die and recesses in the disc dies forming compartments for receiving the inner ends of said link dies,

means for urging said link dies into said compartments,

mean-s for limiting the rotation of said disc dies and foot die, and

means for rotating said disc dies and foot die to the limits of rotation to position the dies to mate in a rectangular configuration.

4. A mandrel in accordance with claim 3 wherein the angular indentations above the neutral axis have upper surfaces parallel to the ends of the tube after bending.

5. A mandrel in accordance with claim 3 wherein the disc die having the convex surface and recess has a side extending between said convex surface and said recess parallel to an end of the tube after bending.

6. A mandrel for supporting a tube during a seamless miter bending operation wherein the end portions of the tube are bent relative to the central portion at a predetermined angle comprising a pair of rectangular bars,

a pair of disc dies rotatab-ly mounted on the ends of the bars, one of said disc dies having a convex projection and the other of said disc dies having a cornplementary interlocking concave portion, each of said disc dies having an'indentation adjacent the upperside of the tube with an upper surface formed parallel to the predetermined angle of the bent ends of the tube, and

a pair of slide dies slidably secured to the bars for supporting the underside of the tube during bending, each of said slide dies, disc dies, and bars defining a relief cavity which decreases in size during bending.

References Cited by' the Examiner UNITED STATES PATENTS 4/1958 Fuchs et a1. 72398 4/ 1959 Fuchs et a1. 72-466 

1. A RECTANGULAR MANDREL FOR SUPPORTING THE INNER WALLS OF A RECTANGULAR TUBE DURING THE BENDING COMPRISING A PAIR OF RECTANGULAR BARS, A PAIR OF DISC DIES ROTATABLY MOUNTED ON THE ENDS OF THE BARS, ONE OF SAID DISC DIES HAVING A CONVEX PROJECTION AND THE OTHER OF SAID DISCS DIES HAVING A COMPLEMENTRY INTERLOCKING CONCAVE PORTION, EACH OF SAID DISC DIES HAVING A RECESS ADJACENT THE UNDERSIDE OF THE TUBE, A PAIR OF SLIDE DIES SLIDABLY SECURED TO THE BARS FOR SUPPORTING THE UNDERSIDE OF THE TUBE, A PAIR OF LINK DIES PIVOTALLY MOUTED ON THE ENDS OF THE SLIDE DIES, AND MEANS FOR URGING THE ENDS OF THE LINK DIES INTO THE RECESSES IN THE DISC DIES. 